You are dwelling in the past instead of looking into the future...
Look at who Mihawk will face - Zoro, who will have heads of top tiers in a bag by the time he fights Mihawk.
Oda is making Zoro the greatest swordsman ever and the hardest challenge he will give him is going to be Mihawk.
Not Vista, not Shanks, not an Admiral or anyone else.
Yonkos can split the heavens all they want, when that feat actually does something useful in a fight, I might praise it.
His title means exactly what it means - the strongest swordsman in the world, above any other swordsman.
Your mistake is thinking that devil fruits are superior to swords or that someone has better haki than Mihawk.
You can wank feats but you will have to do a 180° when Mihawk shows his, which will make you into a bad power scaler.